Posted
by
samzenpus
on Wednesday October 08, 2008 @11:27PM
from the flame-on dept.

GogglesPisano writes "UK geneticist Steve Jones gave a presentation entitled Human Evolution Is Over. He asserts that human beings have stopped evolving because modern social customs have lowered the age at which human males have offspring, which results in fewer of the mutations necessary to drive evolutionary change. Apparently the fate of our species now depends upon older guys hooking up with younger woman. I, for one, welcome this development."

The author makes two additional points that the summary doesn't mention. Firstly, children born in the west are dramatically more likely to survive. They experience significantly less natural selection. Secondly, our large populations make any genetic fluke less likely to survive. Think of inbreeding here; with a small population, otherwise rare genes can become common. We're experiencing the reverse trend.

There's a blog post from PZ Myers on Pharyngula that addresses this statement from Steve Jones fairly well I think. Read it in full here [scienceblogs.com]

This[the idea that older men have more mutations in their sperm] is true, but it makes no sense. It's not as if younger fathers produce no mutations -- they generate plenty. It's a difference in degree, nothing more, so we still have plenty of new mutations percolating into the population. And of course, over most of human history parents have been relatively young, since you couldn't count on living to the age of 35.

And then there's this odd argument.

Another factor is the weakening of natural selection. "In ancient times half our children would have died by the age of 20. Now, in the Western world, 98 per cent of them are surviving to 21."

That makes even less sense. Natural selection is going to eliminate variants; by reducing its effects, we permit more mutations to persist in the population. One moment he's complaining that fewer mutations are being produced, the next he's complaining that the mutants are thriving. Which is it?

Bacteria, for example, reproduce at age 1 hour, say, and have no trouble evolving.

Bacteria also reproduce in an exponential fashion, given an adequate supply of food. In one day a single bacterium will turn into 2^24 bacteria for a total number of 16,777,215 divisions per day or 6,123,683,475 times per year. That's far more than the 300 or so divisions for the 29-year old mentioned in the article, a rate of around 1 per year. This means that a single bacterium mutates around 6 billion times faster than a human.

Yes, this is an extreme (and simplified) estimate but it does give you an idea of the difference in scale between bacterial evolution and human evolution. It has nothing to do with absolute time, it has to do with the overall number of cell divisions over time.

Bacteria are also very good at picking up genes from other bacteria in their environment, which is another way that they evolve. Bacteria also often live in environments with little protection from outside influences such as chemicals and radiation. Our bodies have fairly complex mechanisms to prevent and weed out mutations but bacteria mostly lack this ability.

These are just some of the reasons that bacteria generally evolve much faster than humans.

I agree, but usually those "saved" people don't breed or become uncapable of.

1000 years ago, a child who developed diabetes would probably die long before they were able to reproduce. If they were lucky, and had parents wealthy enough to afford the best medical care the times could provide, they might live into their early twenties. Now, of course, a diabetic child can grow up to live a happy, healthy, normal life, including raising a family.

Human mind is not a clean slate. This has not been the consensus since the 60s.

The aptly titled book "The blank slate" by Steven Pinker is a really good overview of the research that has evolved our understanding of the nature and nurture debate.

There are genetic factors that influence intelligence, as well as environmental factors. The notion that everyone is born equal is unfortunately not true. (people are much more accepting that physical differences are genetic, but not mental...)

I see what you are trying to say - but your point doesn't apply as you think it does. As creatures get longer dna / live longer (note: these two are not related but both increase mutations), their dna correction mechanisms improve, a necessity to avoid mutational meltdown (http://en.wikipedia.org/wiki/Mutational_meltdown). So in essence the amount of mutations that humans would pass onto the next generation at their (pre-civ) average breeding age is the same as for cats or squirrels at their average breeding age.

All creatures hover around the 1 (on average) for each offspring - as this nets you the best rate of evolution vs stability (although in crisis situations a higher mutation rate might be beneficial / opposite case as well)

As has already been said, sex is the major innovator in genetic diversity, so mutation - as measured separately from the DNA-swapping that goes on during sex - is less relevant to our future.

And considering that the current theory of why sex exists - to counter diseases that come to exploit our genome - it's interesting to note that disease itself will always play a major role in our shifting genome. Climate change is already making diseases spread more rapidly - because lack of overnight freeze leaves more vectors thriving.

Even though we medicate our sick, diseases will always evolve. In fact, they evolve faster *because* of this, which means that those members of the human race who can't get medication will have to evolve to survive.

1) The idea is based on genes being switched on and off by conditions in the environment. For example a group of genes associated with resistance to mutations caused by radiation are switched on by exposure to radiation.

2) genetic mutations accumulated in males, at least up to the age of puberty, are passed onto the sperm. The theory is that this includes which genes are switched on or off. Hence environmental factors affect the genes passed on by males.

3) eggs are fully formed when the female is in the womb, so no mutations are passed on. Hence environmental factors do not affect the genes passed on by females.

4) Natural selection only works if you have a fitness criteria. Just having lots of variants is no different from having few variants unless there is a fitness criteria by which successful variants are selected.

Neither donkeys nor apes existed when humans and apes took divergent paths from the common human / ape ancestor, so your attempt at sarcasm would have been far better if you knew what you were talking about.

Darwin didn't claim humans evolved from apes. Modern evolution theory doesn't claim that humans evolved from apes. And apes, humans, and donkeys do indeed have a common ancestor, just like frogs and elephants have a common ancestor, and sharks and redwood trees have a common ancestor.

The biggest driver of evolution will always be catastrophic changes to the environment. Evolution advances rapidly when space in made available for mutations develop into empty spaces within the food chain in specific locals. It is very likely that the biggest driver for human evolution has been the relatively frequently recurring ice ages in recent geologic history.

Just as in future, the major drivers for human evolution will be those same ice ages recurring or, on own impact upon the environment being so great as to alter the environment sufficiently from the conditions under which we evolved as to force evolutionary adaptation to the new altered environment. Other changes in bacteria or viruses could also force associated changes in humans and, of course not to forget catastrophic impact.

Although evolution occurs across millions of years, there will be numerous periods, millennia, where evolution is accelerated fro particular species due to particular environmental conditions, so not much gradual change, but periods of relative stability interspersed with periods of accelerated change.

So as it has occurred in the past, a catastrophic event will either accelerate human evolution or end it, extinction being the only reason for a species to cease evolving. Crazy short haired rock throwing monkeys are really going to have to get over the idea that this universe needs or wants them to survive;D.

I actually attended the lecture, and people are talking the most amazing rubbish about it.
It focussed on three parts:

Mutation

Natural selection

Isolation

Mutation is going down because the window of reproduction in society is narrowing - men tend have children in a narrow 5-year band at around age 35-40. It's older men who engender more mutation through genetic drift (which increases through age).
Natural selection - people are living to reproduce more than ever before. In Darwin's time, 33% of people survived to breed. Now it's 99% in the West. It doesn't matter if you have a advantageous OR disadvantageous mutation now, you still breed.
Isolation - more isolated populations allow a trait to spread. The world is clearly one big melting pot when it comes to human breeding, so isolated populations can't develop.
His final point: this means that evolution is not really happening any more.

This is the reason that taxonomists now use genetic information rather than morphology, as the latter can lead to erroneous classifications (something that's happened quite a lot in the past).

No kidding.

I find the whole concept of "species" to be flawed in this respect. The only practical way to describe relationships between populations (*not* species) is the genetic differential between those populations.

The whole concept of "species" is part of what drives the creation science crowd. "Oh, but you've never witnessed speciation!" Yeah, that's because there's no such thing as speciation. It's an artificial term that represents the false concept of species!

All we have is variance of alleles within different populations. We don't have "species." Evolution is nothing more than the changes in allele occurrence in a populations over time.

And to get back to the stupid-head article, that is still happening in humanity. As for all of you folks saying that medicine has stopped evolution in humans, that's ridiculous. We still have selection pressures, though those selection pressures may be minimal. All we're doing is allowing a massive amount of genetic diversity within our populations. The next time selection pressure shifts (and it will -- it always does), we'll have a *lot* of genetic variation ready to meet the challenge.

This is all simple evolution. Most of you probably studied the exact same thing in junior high, with the decrease in wolves leading to an increase in rabbits, and then the wolves ramping up again to kill off the rabbits, and so on. This cycle (which is highly simplified) is what we're experiencing now. At some point, our environment will change, and we'll be glad to have all the genetic diversity we're building up now.